Device for measuring and indicating changes in resistance of a living body

Abstract

A device for measuring and indicating changes in the resistance of a living body including a single battery source, a means for setting a reference voltage level provided across the battery, a unity gain high input impedance and low output impedance buffer amplifier having as its input the reference voltage level, a balanceable resistance bridge having the output of the buffer amplifier applied thereto and having the living body coupled thereto as a part of the bridge, a meter amplifier for amplifying any imbalances in the bridge caused by changes in the resistance of the living body and a meter coupled to the output of the meter amplifier for indicating the changes in resistance of the living body.

I claim: 
     
       1. A device for measuring and indicating the changes in resistance of a living body comprising; a single battery;   a means for setting a reference voltage level provided across the battery;   a unity gain high input impedance and low output impedance buffer amplifier having as its input the reference voltage level;   a balanceable resistance bridge having the output of the buffer amplifier applied thereto, said bridge being arranged such that the living body is couplable thereto as part of said bridge;   a meter amplifier for amplifying any imbalances in the bridge caused by changes in the resistance of a living body when said living body is coupled thereto; and   a meter coupled to the output of the meter amplifier for indicating the changes in resistance of the living body when said living body is coupled to said bridge.   
     
     
       2. A device according to claim 1 wherein said means for setting a reference voltage level comprises at least one ordinary diode. 
     
     
       3. A device according to claim 2 wherein a light emitting diode for indicating that said device is on is provided in series with said ordinary diode. 
     
     
       4. A device according to claim 3 wherein said single battery source not only provides said reference voltage level but also powers said buffer amplifier and said meter amplifier. 
     
     
       5. A device according to claim 4 wherein said meter amplifier comprises an operational amplifier having a feedback circuit such that the feedback is proportional to current in said meter and said amplifier acts as an undamped current source. 
     
     
       6. A device according to claim 5, wherein said living body is couplable to said bridge via a jack electrically coupled to said bridge and a plug for insertion into said jack, said plug being coupled to electrodes for coupling said living body to said plug. 
     
     
       7. A device according to claim 6 wherein said jack is a normally closed jack and a calibration resistor is coupled to said jack such that when said plug is removed from said jack, said calibration resistor is coupled to said bridge. 
     
     
       8. A device according to claim 7 further comprising a multi position switch means for turning said device on and off and for connecting said battery to said meter such that the condition of said battery can be read on said meter. 
     
     
       9. A device according to claim 8 further comprising a battery charging means, said battery charging means comprising a battery charger coupled to a charging plug inserted into said jack after said plug coupled to said electrodes is removed and said multi-position switch means is in an off position. 
     
     
       10. A device for measuring and indicating the changes in resistance of a living body comprising: a single battery;   a resistive means for setting a reference level provided across said battery;   a unity gain high input impedance and low outputed impedence buffer amplifier having as its input the reference voltage level, said buffer amplifier comprising an operational amplifier;   a balanceable resistance bridge having the output of said buffer amplifier applied thereto, said bridge being arranged such that the living body is coupleable thereto as part of said bridge;   a female jack electrically coupled to said bridge and a male plug for insertion into said jack, said plug being coupled to electrodes for coupling said living body to said plug;   a calibration resistor coupled to said jack such that when said plug is removed from said jack, said calibration resistor is coupled to said bridge;   a meter amplifier for amplifying any imbalances in the bridge caused by changes in the resistance of a living body when said living body is coupled thereto, said meter amplifier being powered by said single battery and comprising an operational amplifier having a feedback circuit such that the feedback is proportional to current in a meter and said amplifier acts as an undamped current source; and   a meter coupled to the output of the meter amplifier for indicating changes in resistance of the living body when said living body is coupled to said bridge.   
     
     
       11. A device according to claim 10 further comprising a battery charging means comprising a battery charger coupled to a charging plug inserted into said jack after said plug coupled to said electrodes is removed from said jack.